The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Coning in wells is a common problem which includes, but is not limited to, water coning and gas coning. Water coning in oil wells occurs when the water beneath an oil-bearing zone encroaches the oil-bearing zone. This may be due to the rate of oil extraction or “drawdown” that results when the oil is being produced. The water may enter the well perforations so that it is produced with the oil. Eventually, the water encroachment may be significant enough so that very little or no oil is produced. Gas coning can also be a problem in oil and water wells. Gas coning is based upon the same principles as water coning. Gas can cone downward and occlude the perforations decreasing and eventually preventing liquid production.
In many oil and gas fields, water production may exceed oil production. In some of these areas, reservoir drive is low and total reservoir fluid production may be less than 100 bpd (<15.9 m3/day). Many depleted reservoirs may fall into this category. Wells under these conditions often do not have the economic potential to support the cost of water control remediation/intervention services as they exist today. High oil extraction rates, in otherwise productive wells, may also result in undesirable water production.
Efforts to preempt or postpone water production typically involve perforating the wellbore as far above the water-bearing zone as possible and producing oil below the critical oil production rate. In many instances, producing below the critical oil rate may be uneconomical. This was first described by Muskat and Wyckoff. See Muskat, M. and Wyckoff, R. D.: “An Approximate Theory of Water-Coning in Oil Production,” Trans. AIME (1935). Johns et al more recently presented an improved treatment of this problem providing analytical solutions for cases of both upward and downward coning (SPE 77772).
Current methods used to prevent or reduce unwanted fluid production include injecting a “blocking” or “plugging” agent that effectively blocks off or seals the undesirable fluid zone. Various polymers and gels have been used for this purpose. Blocking agents may be injected into the formation in a non-swollen or a non-precipitated state. In the case of water coning, the blocking materials will swell or precipitate, thus plugging or blocking off the area from further water influx. When treating gas coning, foamed gels have been used. The use of these materials may have some disadvantages, however. Such treatments may be rather costly and it is difficult to place the blocking materials to sufficiently seal off a large enough area around the wellbore for them to be effective. Furthermore, the blocking treatment may be ineffective when fissures or fractures are present in the formation. If clean-up of the materials is necessary, these materials may be difficult to remove. And in some cases, these materials may inadvertently result in permanent blocking or plugging of the desired production zone.
Because of the shortcomings of these various methods, new methods and improvements to control unwanted fluid flow from subterranean formations are needed.